Because polychlorinated biphenyls (PCB's) have been found to be environmental pollutants, their use as an insulating fluid in transformers, capacitors, and other electrical equipment is no longer permitted. One of the fluids which has been substituted for the PCB's is perchloroethylene, C.sub.2 Cl.sub.4. Perchloroethylene has been chosen as a substitute for PCB's because it has good dielectric properties, is non-flammable, and remains fluid at low temperatures. One of the difficulties encountered in the use of perchloroethylene, however, has been the tendency of insulation to blister in the presence of that fluid. This is especially a problem with epoxy powder coatings which are applied to copper wire. The blistering is regarded as a serious problem in the use of perchloroethylene as it can lead to the electrical failure of the apparatus.